DHCP and BootP

General

The DHCP (Dynamic Host Configuration Protocol) and BootP (Bootstrap
Protocol) pass network configuration information to a host during
startup. In NetDB3, DHCP is configured on node and network records. For node records, a unique hardware address must be entered to configure
DHCP.

DHCP is also described in Internet RFCs 2131 and 2132. Note that
BOOTP is a subset of DHCP commands.

DHCP information is updated from NetDB approximately every 10
minutes.

DHCP flag (node record)

When you check the DHCP box and enter a hardware address in NetDB, the
campus DHCP servers will reply to a DHCP request from that
address. The servers also return default DHCP options or additional options if they're specified in the
NetDB record.

Roaming flag (node records)

Roaming DHCP allows machines to move to other
networks without requiring manual configuration of IP addresses. If
you check the Roaming box, you enable Roaming DHCP for that hardware
address. If the machine moves to another network that offers available
roaming DHCP addresses, the DHCP server will give one of these addresses
to the mobile machine.

Default Node DHCP options

The default node DHCP options at Stanford University are IP
address, subnet mask, gateway, domain name, and domain name servers. The
option numbers come from RFCs 2131 and 2132.

Additional DHCP options

In NetDB, you can also set the following additional DHCP options for node interfaces, networks, or address spaces. Note: Use with
caution as improper use may cause networking problems. The
syntax for options is <dhcp option> = <value>.

DHCP Option

Option Number

Node Interface

Net

Address Space

Description

next-server

Y

Y

Y

boot/config server

tftp-server-name

66

Y

Y

Y

TFTP boot/config server

filename

67

Y

N

Y

boot/config file - e.g. thin clients

log-servers

7

Y

Y

Y

domain-name

15

Y

Y

Y

e.g., stanford.edu

domain-name-servers

5

Y

Y

Y

DNS servers

netbios-name-servers

44

Y

Y

Y

WINS servers

netbios-node-type

46

Y

Y

Y

1=B, 2=P, 4=M, 8=H

option-144

144

Y

N

N

for HP printers

permit*

N

N

Y

see below

max-lease-time

Y

Y

Y

default-lease-time

51

Y

Y

Y

DHCP lease time (currently 2 days)

*By default, the DHCP service only responds to known clients — for example, nodes with their hardware addresses listed in NetDB. The permit
DHCP option can override this default on a per-address space
basis. A value of unknown-client allows
both known and unknown clients to use DHCP in a
particular address space; a value of only-unknown-client allows only unknown clients to use DHCP in a
particular address space. The latter is useful for setting up networks
with separate address spaces for known and unknown DHCP clients.